Polydopamine-Mediated Anchoring of Pd on Magnetic Ni@CNTs: A Robust Core–Shell Nanocatalyst for Recyclable Heck Cross-Coupling

The development of high-performance, magnetically recyclable nanocatalysts remains challenging, primarily due to the poor stability and inadequate control over active metal dispersion in conventional magnetic supports. To address these limitations, we designed a Ni@CNTs@PDA–Pd catalyst through innovative interfacial engineering. Carbon nanotube channels effectively encapsulate and protect magnetic nickel nanoparticles, while a polydopamine (PDA) coating enables uniform dispersion of palladium nanoparticles (2.0 ± 0.7   nm). The catalyst exhibits strong superparamagnetism (6.64   emu·g⁻¹), allowing efficient magnetic separation. In Heck reactions, it achieves a turnover frequency (TOF) of 958   h⁻¹ and retains 89.5% conversion after ten cycles, outperforming most reported Pd/CNT and magnetic catalysts. Density functional theory (DFT) calculations reveal that although Ni encapsulation increases the electron density of the CNT surface—which may hinder Pd deposition—the PDA interlayer counteracts this effect via strong coordination bonds, ensuring excellent Pd stabilization. This study provides key insights into electronic metal–support interactions and offers a scalable strategy for designing high-performance magnetically recyclable catalysts. It highlights the active role of the magnetic core in modulating the electronic environment of catalytic sites and underscores the critical synergy between the core, shell, and active metal in rational catalyst design.